Integrated electrode maintenance for robotic welding cell including cap extractor

ABSTRACT

A cap extractor for a welding gun includes a housing, a pair of springs, and first and second arms that are arranged between the springs. Each of the first and second arms have teeth that are configured to engage a welding cap. The first and second arms are configured to move relative to the housing in first and second directions that are transverse to one another by deflecting the springs.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application is a continuation of PCT Application No.PCT/CA2018/050702 filed Jun. 12, 2018, and is incorporated herein byreference.

BACKGROUND

The disclosure relates to tool maintenance assembly used to remove,replace and dress the caps of a welding gun.

A pedestal welding gun station is a fairly common robot cell elementthat incorporates a resistance welding gun in a position that makes itaccessible to one or more industrial robots. The industrial robot isused to manipulate an assembly of sheet metal stampings for presentationto one or more pedestal-mounted welding guns, or other equipment in therobot cell.

In the resistance spot welding process, a pair of copper alloyelectrodes squeeze together on overlapping metal sheet(s) at thelocation a resistance spot weld is desired. The face geometry of thespot welding electrodes is selected based on the workpiece material(s)and thickness, desired weld size, and other process factors such as heatbalance, weld appearance, and the presence of coatings, adhesives, orsealants. After sufficient force has been applied to bring the surfacesto be welded into intimate contact, a precisely controlled electricalcurrent is passed between the copper alloy electrodes so it causesheating in the workpiece to achieve the weld.

The face of electrodes are subjected to significant localized heating,mechanical forces, and material interactions. The result is chemical andphysical changes that affect the electrical conductivity of the weldingelectrodes and the concentration of heating and force. Some compensationis usually provided by automatic adjustment of resistance weldingcontrol parameters. At some point, it becomes necessary to eitherrefurbish the electrode face or replace the electrode.

Most prior art involves tools that are manually operated or accessed bya robot mounted resistance welding gun. Pedestal-mounted welding gunsare sometimes fitted with tip dressers that swing into a maintenanceposition, which is in the path of the closing welding electrodes. Whenthe robot performs material handling, the full range of electrodemaintenance tools does not appear to have been previously considered.

SUMMARY

In one exemplary embodiment, a welding station includes a welding gunthat includes first and second electrode caps. The welding gun ismovable between a working position and a maintenance position. Theworking position corresponds to a welding operation on at least oneworkpiece. A maintenance tool assembly is configured to cooperate withthe first and second caps in the maintenance position. The maintenancetool assembly includes a cap extractor, cap dispensers and a capdresser. The cap extractor is configured to remove the first and secondcaps from the welding gun. The cap dispensers are configured to providenew caps to the welding gun for installation. The cap dresser isconfigured to shape the electrode cap faces. The maintenance toolassembly includes a lift actuator. A translate actuator is respectivelyconfigured to move the maintenance tool assembly in the lift andtranslate directions with respect to the welding gun.

In a further embodiment of any of the above, the maintenance toolassembly includes a plate that supports the cap extractor, the capdispensers and the cap dresser. A platform is mounted to a pedestal thatpivotally supports the weld gun for rotation between the working andmaintenance positions. The translate actuator is configured to slide theplate relative to the pedestal along slide ways.

In a further embodiment of any of the above, the lift actuator isarranged between the plate and platform and is configured to lift theplate relative to the platform.

In a further embodiment of any of the above, the cap extractor includesa housing and a pair of springs. First and second arms are arrangedbetween the springs. Each of the first and second arms have teethconfigured to engage a welding cap. The first and second arms areconfigured to move relative to the housing in first and seconddirections transverse to one another by deflecting the springs.

In a further embodiment of any of the above, the cap dispensers includea sleeve that slidably receives a drawer configured to house a column ofweld caps. A spring cooperates with a slide block arranged in thedrawer. The spring urges the slide block toward an aperture in thedrawer that is configured to receive a welding gun electrode adapter.

In one exemplary embodiment, a method of operating a welding stationincludes a welding gun that is pivoted from a welding position to amaintenance position. A worn welding cap is extracted from the weldinggun in the maintenance position. A new welding cap is installed on thewelding gun in the maintenance position. A worn or new welding cap isdressed in the maintenance position.

In a further embodiment of any of the above, the method includes thestep of translating a maintenance tool assembly between cap extracting,cap dispensing, and cap dressing positions, which respectively providethe extracting, installing and dressing steps.

In a further embodiment of any of the above, the maintenance toolassembly is supported on a plate and includes the step of lifting orlowering the maintenance tool assembly during at least one of theextracting, installing and dressing steps.

In a further embodiment of any of the above, the method includes thestep of sensing the presence of the new welding cap subsequent toperforming the installing step.

In a further embodiment of any of the above, the method includes thestep of sensing the absence of the old welding cap subsequent toperforming the extracting step.

In a further embodiment of any of the above, the method includes thestep of sensing the newly installed welding cap presence subsequent toreturning the welding gun to the welding position.

In one exemplary embodiment, a cap extractor for a welding gun includesa housing, a pair of springs, and first and second arms arranged betweenthe springs. Each of the first and second arms have teeth configured toengage a welding cap. The first and second arms are configured to moverelative to the housing in first and second directions transverse to oneanother by deflecting the springs.

In a further embodiment of any of the above, the first and second armsare mounted to spaced apart disks. The first and second arms arepivotally connected to one another by a spacer pin that rotationallyaffixes the disks to one another.

In a further embodiment of any of the above, the springs are wavesprings. Each wave spring is received in a recess of one of the disks. Acollar is arranged between each disk and the housing to locate arespective wave spring relative to the housing.

In a further embodiment of any of the above, an actuator is pivotallyattached to the housing. The actuator is operatively connected to thefirst arm to rotate the first and second arms along with the disks. Theactuator is configured to articulate relative to the housing duringrotation of the first arm in the housing.

In a further embodiment of any of the above, a biasing spring isinterconnected to the first and second arms to urge the first and secondarms toward one another.

In one exemplary embodiment, a method of removing a cap from a weldinggun includes a welding cap having a centerline received between teeth offirst and second arms. The arms float along the centerline and arelateral relative to the centerline during the receiving step to permitalignment between the teeth and the welding cap. The welding cap istwisted from a welding gun.

In a further embodiment of any of the above, the method includes thestep of normally biasing the first and second arms toward one another.The receiving step separates the first and second arms.

In a further embodiment of any of the above, one of the first and secondarms abuts a stop to precede the receiving step. One of the first andsecond arms is spaced from the stop during the twisting step.

In a further embodiment of any of the above, the first and second armsare supported between disks. The first and second arms include the stepof the disks supported by springs. The floating step includes deflectingat least one of the springs.

In a further embodiment of any of the above, an actuator is pivotallymounted to a housing which contains the first and second arms. Thetwisting step includes articulating the actuator relative to the housingand rotating the first and second arms relative to the welding gun.

In one exemplary embodiment, a cap dispenser for a welding gun includesa sleeve that slidably receives a drawer configured to house a column ofweld caps. A spring cooperates with a slide block arranged in thedrawer. The spring urges the slide block toward an aperture in thedrawer that is configured to receive a welding gun electrode.

In a further embodiment of any of the above, the spring is a clockspring wound about a drum. The drum is mounted to a roller pin securedto a spring housing arranged on the sleeve. One end of the clock springis connected to the slide block.

In a further embodiment of any of the above, the drawer includes a rampthat selectively cooperates with a movable pin mounted to the sleeve.The pin is configured to maintain the drawer within the sleeve andresist the clock spring.

In a further embodiment of any of the above, the spring urges the drawerto an extended position relative to the sleeve.

In a further embodiment of any of the above, the cap dispenser includesa sensor mounted relative to the drawer and configured to detect a weldcap orientation relative to the aperture.

In one exemplary embodiment, the method of dispensing caps for a weldinggun includes a weld cap which is biased to an aperture in a dispenser. Aweld gun electrode adapter is inserted through the aperture to engagethe weld cap.

In a further embodiment of any of the above, the biasing step includesthe weld cap which is urged toward the aperture with a slide blockconnected to a spring.

In a further embodiment of any of the above, the cap dispenser includesthe step of providing a column of weld caps within a drawer that isslidably received in a sleeve. The slide block is arranged in thedrawer.

In a further embodiment of any of the above, the cap dispenser includesremovably retaining the drawer relative to the sleeve. The drawer isreleased relative to the sleeve to load more weld caps.

In a further embodiment of any of the above, the cap dispenser includessensing an orientation of the weld cap that is sensed within thedispenser. The cap dispenser provides a weld cap orientation signal to acontroller for monitoring.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be further understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 schematically illustrates a welding station.

FIG. 2 depicts a welding gun and maintenance tool assembly integratedwith one another on a pedestal.

FIG. 3 schematically illustrates the maintenance tool assembly, whichincludes a cap extractor, a cap dresser, and cap dispensers.

FIGS. 4A-4D illustrate the maintenance tool assembly in cap extracting,first and second cap dispensing, and cap dressing positions,respectively.

FIG. 5 is a schematic depicting a control system for the welding stationincluding welding gun and maintenance tool assembly controls.

FIGS. 6-9 illustrate perspective, front, side, and cross-sectionalviews, respectively, wherein the cross-sectional view is taken alongline 9-9 in FIG. 8.

FIGS. 10-12 are perspective, exploded, and cross-sectional views,respectively, of the cap extractor, wherein the cross-sectional view istaken along line 12-12 of FIG. 10.

FIGS. 13A-13C are cross-sectional views along line 13-13 of FIG. 10 and,respectively, of first, second, and a third cap extracting positions.

FIG. 14 is a perspective view of first and second cap dispensers.

FIGS. 15A-15B, respectively, are views of a cap dispenser in extendedand exploded positions.

FIG. 16 is a cross-sectional view of the cap dispenser in an extendedposition.

FIG. 17 is a cross-sectional view of the cap dispenser in a closedposition.

FIG. 18 is an enlarged cross-sectional view of a cap in an improperlyloaded position within the cap dispenser, triggering a fault code.

The embodiments, examples and alternatives of the preceding paragraphs,the claims, or the following description and drawings, including any oftheir various aspects or respective individual features, may be takenindependently or in any combination. Features described in connectionwith one embodiment are applicable to all embodiments, unless suchfeatures are incompatible. Like reference numbers and designations inthe various drawings indicate like elements.

DETAILED DESCRIPTION

A welding station 10 is schematically illustrated in FIG. 1. One examplestation 10 includes a load fixture 12 that establishes the position ofworkpieces 14 at the entrance to the welding station 10. The weldingstation 10 includes a robot 18, which may be enclosed by a perimeterfence 16 for safety.

Workpiece 14 may be placed into the load fixture 12 by an operator orautomation. The robot 18 may retrieve workpiece 14 from the load fixture12 using robot end of arm tooling 20 that holds the workpiece in thedesired orientation and configuration. A welding gun 22 is mounted to abase 24 and spot welds the workpiece 14, for example.

The welding gun station is commonly employed within robot cells for bothspot and projection welding. Such robot cells employ one or morematerial handling robots to manipulate the workpiece(s) instead of theheavy resistance welding gun. This enables the use of smaller, moreagile, and less expensive robots to automate the process. This robotcell configuration is also useful when the process involves multipleresistance welding guns that may be different sizes, configurations, ororientations. Or it may enable the robot to manipulate a workpiecebetween a number of stations employing different processes necessary tocomplete an assembly. Processes could for example include metal working,coating application, arc welding, fastener welding, assembly, andinspection.

The fence 16 can provide isolation between the robot cell and theelectrode maintenance station including a maintenance tool assembly 26for removing, installing and/or dressing the welding gun electrodes.This barrier would prevent the process on one side from affecting theother. It would therefore permit operations such as manual electrodemaintenance or replacing the electrode dispensers to occur withoutinterrupting the robot cycle.

A maintenance tool assembly 26 is mounted to the base 24. Periodically,the welding gun 22 may be pivoted in a rotational path R to bring thewelding “electrodes”, “tips” or “caps” of the welding gun 24 to themaintenance tool assembly 26 for replacement and/or dressing. While itis possible in alternative configurations to pivot the welding gun toposition the electrodes for extraction or replacement, the disclosedconfiguration illustrated employs a simple longitudinal translation T tomove the tools. This improves the repeatability, control, and sensing ofthe welding gun pivot operation. It keeps the welding gun stationaryduring the maintenance operation so there is little chance of accidentalcollisions or unintended motion while in the electrode maintenanceposition.

Referring to FIGS. 1-3, the maintenance tool assembly 26 includes a capextractor 28 and cap dispenser 30 including first and second capdispensers 30A, 30B. A cap dresser 32 is provided at an end of themaintenance tool assembly 26 opposite the cap extractor 28 such that thecap dispenser 30 is arranged therebetween. The described resistancewelding gun is for resistance spot welding but aspects of theconfiguration could be applied to projection welding equipment used toaffix components such as fasteners or spacers.

Generally, a typical sequence would be to present the electrode caps tothe tip dressing station on a regular basis. The frequency depends onthe welding conditions but may be for example every 10, 25 or 100 welds.At that time the tip dresser would use cutters or forming tools to cleanor restore the profile of the electrode cap tip so welding consistencycan be maintained. After a number of these tip dressing cycles have beenperformed, it is necessary to replace the electrode cap with a new one.The replacement frequency may relate to the number of tip dressingcycles, a physical attribute such as electrode cap length, a weldingperformance indicator such as excessive or insufficient welding current,or feedback of weld discontinuities.

A conventional dressing station is included for periodic light cleaningand shaping of the electrode face(s). When dressing of the electrode isno longer appropriate, an electrode extractor and electrode dispensercan be employed to replace the electrode(s).

The resistance spot welding gun station is configured to facilitate therequired electrode maintenance so there is minimal impact on productionthroughput. Electrode maintenance is frequently performed during thetime the industrial robot is executing material handling (i.e.,retrieving workpieces or delivering the completed weldment to the unloadstation) or another function such as in-line inspection. The describedrobotic welding cell module permits maintenance to be performed entirelymanually, or with automation. The electrode maintenance tools aremodular in nature so the system can be reconfigured depending on thebusiness priorities and financial analysis.

The disclosed resistance welding gun is mounted on a pivot unit assemblythat enables the welding electrodes to be presented to a location awayfrom the production area. The pivot is operated by a pneumatic cylinderthat rotates the welding gun between hard position stops. The pivotcould also be operated by a servo drive or other mechanical orelectrical system that facilitates accurate positioning of the weldingelectrodes. The resistance welding electrodes can be serviced when therobot is being utilized to perform the workpiece manipulation. Thisreduces the possibility the robot cell throughput will be affected bythe electrode maintenance operation.

The number and position of maintenance tools can be established to suitthe anticipated electrode maintenance frequency, production rate, orresistance welding cell configuration. The station could include nomaintenance tools to start, where the pivoting mechanism is used aloneto present the welding electrodes outside of the robot cell for manualmaintenance or replacement. An automatic electrode cap dressing toolcould be added for regular lightly cleaning and profiling of the weldingface. Additional tooling stations could be added to provide thecapability to reshape the welding face or to remove and replace a wornout electrode.

The maintenance tools are outside of the production space, which canimprove access to the electrode maintenance tools for servicing (e.g.,emptying chips from the dresser or reloading cap dispenser), put theelectrode maintenance tools in a location that is safer or moreaccessible to the personnel that are necessary to maintain them, permita configuration that allows servicing of the electrode maintenance toolswhile the welding equipment is performing a production sequence, andensure the production cell is not contaminated with errant machiningchips, coolant, or electrode caps.

Referring to FIG. 2, the welding gun 22 includes first and second arms52, 54 carrying first and second electrode adapters 40, 42,respectively. An electrode cap 44 is mounted on each of the first andsecond electrode adapters 40, 42. The caps 44 may be identical or couldhave different sizes and shapes to suit the welding conditions. The base24 is supported by a pedestal 46 arranged within the work area. Thewelding gun 22 is supported with respect to the base 24 by a pivot 48that is rotated between first and second positions by a pivot cylinder50. The first and second positions may be 180° from one another. Thewelding gun is shown in the working position in FIG. 2. The spot weldinggun is moved clear of the welding area by a simple and reliable pivotingmotion, that also positions the welding electrodes within reach of theintegrated electrode maintenance tools. At least part of the timerequired for the off-line electrode maintenance process can be conductedwhile the robot continues to perform a material handling function.

Referring to FIGS. 2 and 3, the cap extractor 28, cap dispenser 30, andcap dresser 32 are mounted to a plate 38 that is carried by a platform34. The plate 38 is slideably mounted to the base 24, which may includenumerous members secured to one another. This translation stage puts thedesired maintenance tool in the required position to service theelectrode(s), which may include lifting the tool between a lowered andraised position to service the lower and upper electrode respectively.The maintenance tool assembly 26 translates along a longitudinaldirection T (FIG. 3) between numerous positions to place the componentsof the maintenance tool assembly 26 in the desired position with respectto the caps 44. The maintenance tool assembly 26 may also move in avertical direction L (FIG. 3) to lift and lower the maintenance toolassembly with respect to the caps 44 during maintenance. Because oneelectrode extractor can be used to remove either electrode cap, thetranslation stage incorporates the vertical lift so either the upper orlower electrode cap can be aligned with the electrode extractor. A bin58 collects the used, extracted caps 44.

FIGS. 4A-4D illustrate various positions of the maintenance toolassembly 26 with respect to the welding gun. Either or both of the firstand second arms 52, 54 of the welding gun 52 may open and close withrespect to one another. In one example, one of the arms is fixed and theother arm articulates to open and close about the workpiece duringwelding operations. In another example, the first and second arms mayboth open and close about the workpiece. The maintenance tool assembly26 lifts or lowers the maintenance tools with respect to the cap 44 andits relative position on the first and second arms 52, 54. In FIG. 4A,one of the caps 44 is inserted into the cap extractor 28. The cap 44 isrotated with respect to its electrode which breaks the cap 44 free fromthe welding gun. With the cap extractor 28 disengaged from the cap 44(by raising or lowering the maintenance tool assembly 26), the cap 44may be released by the cap extractor 28, dropping the cap into the bin58.

Referring to FIGS. 4B and 4C, the electrode adapter 40, 42 without itscap 44 may be inserted into one of the cap dispensers 30A, 30B of thecap dispenser 30. The first and second electrode adapters 40, 42 areclosed about the new cap to seat the cap firmly on the electrode in aninterference fit. Both the caps 44 can be removed from the first andsecond electrode adapters 40, 42 by the cap extractor 28 beforeinstalling new caps using the cap dispensers 30A, 30B. Alternatively,the cap may be removed from one electrode adapter 40, 42 by the capextractor and a cap installed onto it before repeating the process forthe other electrode.

The new caps may be dressed by the cap dresser 32, as shown in FIG. 4D.In the example, the caps are dressed simultaneously by closing the firstand second electrodes about an aperture of the cap dresser 32. The capdresser 32 may also be used to periodically dress used caps before theneed to replace the caps 44.

A control system 60 is schematically shown in FIG. 5. The system 60includes an air source 62 that selectively supplies compressed air tovarious components via control valve 66 that are operated by acontroller 64. The air source 62 supplies to a cap extractor cylinder 68of the cap extractor 28, a maintenance tool assembly lift cylinder 70,and translate cylinder 72 of the maintenance tool assembly 26 and thewelding gun pivot cylinder 50. Other types of actuators may be usedinstead of air cylinders, if desired.

The first and second cap sensors 74, 76 (also shown in FIGS. 6-8) may beused to detect the presence or absence of a cap 44 during themaintenance procedure. One or more cap presence detectors 78 may be usedwith the first and second cap dispensers 30A, 30B to detect an improperorientation and fault of a cap 44 within the cap dispenser 30 (FIG. 18).

The motor 80 of the cap dresser 32 is operated by the controller 64.Additionally, the controller 64 may also be used to control and monitorthe welding gun 22 during various welding gun operations, as indicatedin block 82, including tracking when the welding gun is in need of tipmaintenance.

Referring to FIGS. 6-9, the platform 34 is slideably supportive withrespect to the base 24 by a slide assembly 86. The translate cylinder 72moves the platform 34 with respect to the base 24 and the welding gun 22supported thereon between various discrete longitudinal positions (shownin FIGS. 4A-4D) to align the desired components of the maintenance toolassembly 26 with respect to the electrodes and/or caps.

The plate 38 is supported with respect to the platform 34 by guide posts88. A lift cylinder 70 is arranged laterally between guide posts 88 andvertically between the platform 34 and plate 38. The lift cylinder 70raises and lowers the maintenance tool components to their desiredpositions.

The first and second cap sensors 74, 76 may be used to detect thepresence of a cap 44 subsequent to extraction by the cap extractor 28and installation of a new cap by the first and second cap dispensers30A, 30B. If a cap is absent when one should be installed or presentwhen it should have been removed, a fault is indicated.

The cap extractor 28 is illustrated in more detail in FIGS. 10-12. Theextractor cylinder 68 includes a cylinder body 90 housing a piston. Thecylinder body is secured to a mounting plate 92. A rod 94 is connectedto the piston within the cylinder body 90 and extends through themounting plate 92 to a clevis 96.

The extractor cylinder 68 is mounted to a housing 100 by spaced apartpivot pins 102, which enables the extractor cylinder 68 to articulatewith respect to the housing 100 during operation. The housing 100 mayinclude multiple housing portions 100A-100D, collectively referred to as“the housing 100.”

The housing 100 includes apertures 106 for receiving the end of anelectrode adapter 40, 42 with its cap 44. Ends of collars 108 arearranged with the apertures 106, and wave springs 114 are arrangedconcentrically about each collar 108. A pair of spaced apart disks 110have a recess that receives one side of the wave springs 114.

First and second arms 116, 118 are carried by the disks 110. The firstarm 116 has a hole 128 that receives a pin 98 securing the clevis 96 tothe first arm 116. The second arm 118 has an end 124 that is received ina channel 122 of the first arm. The first and second arms 116 and 118are pivotably secured with respect to one another by a spacer 112 thatspaces the disks 110 with respect to one another and ensures that theyrotate together with respect to the housing 100. Another spacer 112 isreceived within a slot 120 in the second arm 118. In the example, threespacers 112 are circumferentially spaced with respect to one another androtationally affix the disks 110 to one another.

A biasing spring 126 interconnects the first and second arms 116, 118 tourge them toward one another, in turn, bringing complementary teeth 134toward one another to engage the cap 44. A stop 130 provided on thehousing portion 100A limits the travel of the second arm 118 duringrotation via a stop pin 132 carried thereon.

The wave springs 114 enable the disks 110 to float within the housing100 better ensuring alignment with the teeth 134 and the cap 44. Thatis, there is some flexibility provided by the wave springs 114 to enablethe disk 110 and the associated first and second arms 116, 118 to floatboth laterally and vertically. Thus, absolute precise alignment betweenthe caps and the cap extractor 28 is not required for effective capextraction.

The extraction jaw mechanism floats in a plane normal to the center axisof the jaws. This allows the central axis of the extractor jaws to move,if required, to be coincident with the axis of the electrode taper. Thisprevents a binding force between the taper surfaces that could otherwisebe created during rotation when the two axis are not aligned. Increasedsurface friction due to binding may inhibit axial movement necessary toseparate the electrode from the adapter. Such position variation mayarise from inaccuracy of the positioner or by bending or deflection ofthe welding gun or its components. When the electrode is positioned byautomation or an industrial robot, the electrode could be misalignedwith the cap electrode extractor due to position teaching inaccuracy,positioning repeatability deviation, or deflection within the mechanicalsystem.

The jaw mechanism floats in the direction of the taper axis. Thispermits the strain in the electrode and adapter tapers to aid inreleasing the taper engagement. The intimate engagement of the tapers ismaintained by stress on the material, which causes one or both of thecomponents to deform. A female electrode cap taper for example willexpand (stretch) slightly as its taper is engaged over the male taper ofthe electrode cap adapter. This strain applies a force on the two tapersurfaces to lock them together. On a common ¾″ (19 mm) diameter femaleelectrode, the distance between initial engagement and locking of thetapers may be 1/16″ (1.5 mm). Mounting of the extractor jaw mechanismbetween the wave springs 114 provides the electrode cap the freedom tomove in the direction of the taper axis. By permitting this movement,when the electrode cap is rotated to break the static friction betweentaper surfaces, the strain on the taper helps to urge the tapers apart.This ensures the electrode is consistently released from the adapter.

Since the cap extractor 28 is accessible from either side it is notnecessary to change the welding gun orientation for a single tool toextract either the upper or lower electrode.

First, second, and third positions of the cap extractor are respectivelyillustrated in FIGS. 13A-13C. For better visualization, in FIG. 13A, thearcs A1 and A2 illustrate the path along which the pin 98 and stop pin132 move during cap extraction. The spacer 112 interconnecting first andsecond arms 116, 118 move along a circular path C with the rotation ofthe disks 110. The “+” along these paths indicate the elements positionin the first, second and third positions.

Referring to FIG. 13A, the extractor cylinder 68 is shown with thepiston in a fully retracted position such that the first and second arm116, 118 are maximally spaced with respect to one another to betterfacilitate accommodating the cap into the cap extractor. In thisposition, the stop pin 132 engages the stop 130. Once the cap 44 hasbeen positioned between the teeth 134, the extractor cylinder 68 beginsto close from the first position shown in FIG. 13A to the secondposition shown in FIG. 13B, which more tightly clamps the teeth 134about the cap 44. In this second position, the stop pin 132 is spacedfrom the stop 130.

Referring to FIG. 13C, the extractor cylinder 68 is actuated to a fullyextended position in which the first and second arms 116, 118 arefurther closed about the cap, finally releasing the cap 44 from itselectrode adapter 40, 42. In this third position, the second arm 118 mayengage one of the spacers 112, which was located between the first andsecond arms. Subsequently, the extractor cylinder 68 is retracted, whichreturns the first and second arms 116, 118 to the first position shownin FIG. 13A. In this position, once the electrode adapter 40, 42 hasbeen moved with respect to the cap 44, the cap will simply drop into thebin 58 beneath.

The technique employed for extracting the electrode caps is simply atwisting motion to break the friction of the engaged tapers. When thecylinder advances, the serrated jaws of the extractor bite into theelectrode cap to impart the rotation. The configuration of the jawmechanism enables it to center to the electrode adapter taper, therebyensuring the applied force is consistent even pressure on theserrations. Prior to the cylinder reaching the limit of rod extension,the cap will have been freed. When the cylinder retracts and the jawsreach the hard stops they will separate and allow the electrode cap tofall into the container provided. If cooling water is released when thecap is removed, it will also be captured by the bin 58.

The first and second cap dispensers 30A, 30B are illustrated in moredetail in FIG. 14. In the example, the first cap dispenser 30A is inidentical construction with respect to the second cap dispenser, onlytheir orientation is different. Thus, the second cap dispenser 30B willbe explained in further detail in connection with FIGS. 15A-17.

The process of installing a new cap is as simple as closing the weldinggun onto the electrode cap. After the friction fit tapers engage,opening the welding gun easily overcomes the sliding friction betweenelectrode caps to remove the electrode cap from the dispenser. As soonas the space occupied by the electrode cap is clear another electrodecap will move towards the outlet.

The cap dispenser is configured for off-line refilling and quickexchange. The dispenser can be made to a standard length or the lengthnecessary to accommodate the number of electrode caps required betweenthe standard service intervals.

The dispenser is easily removed from its holder by pulling the springloaded catch. The dispenser is easily serviced in a similar fashion bypulling the spring loaded catch. There is no cumbersome on-linedispenser loading or replacement process required so dispensers can beloaded off line. This also has the added advantage of easily enablingdifferent electrode caps to be installed in the dispenser when requiredby a different workpiece or welding condition.

A sleeve 136 slideably receives a drawer 138 that houses the caps 44.The drawer 138 includes a ramp 140 that selectively cooperates with apin 144 carried by an end cap 142 mounted to the sleeve. The pin 144 maybe spring loaded to bias the pin 144 inward to engage the ramp 140 whenthe drawer is fully inserted and seated with respect to the sleeve 136.Alternatively, the pin 144 may be threadingly moved into and out of anengagement with respect to the ramp 140. The dispenser is easy to loadsince the tray can be fully opened or partially opened for filling,depending on which method is easiest for a particular size and geometryof welding electrode.

Electrode caps are urged towards the outlet of the dispenser by afollower, which is pulled by a constant force spring. A spring assembly146 is mounted to the sleeve 136 to urge a slide block 156 locatedwithin the drawer 138 in a direction that forces the caps 44 to aposition beneath an aperture 162 in a plate 160. In an example, thespring assembly 146 includes a spring housing 148 having first andsecond housing portions 148A, 148B. The spring housing 148 receives adrum 150 rotatable about a roller pin 152 that secures the housingportions 148A, 148B to one another. A clock spring 154 is affixed to thedrum 150 at one end and to the slide block 156 at an opposite end by afastener 158. The clock spring 154 wraps about the drum 150 in anormally biased position. Thus, the slide block 156 is pulled leftwardas illustrated in FIG. 17 to push the stack of caps 44 toward theaperture 162.

The presence of the cap at the outlet is verified by a sensor, whichconfirms the straight side of the electrode cap skirt is tight againstthe stop. A through beam light sensor is provided to ensure there is aproperly oriented electrode cap at the discharge point. A fiber opticthrough-beam light sensor is referenced, but other sensors can beemployed. The sensor has the secondary function of verifying there is anelectrode cap in the dispenser since the follower is configured so itwill not operate or activate the electrode cap detection sensor.

Referring to FIG. 18, the drawer 138 includes a hole 164 that maycooperate with the cap presence detector 78, which may be a laser. If acap 44 is oriented improperly such that the hole 164 is obstructed, afault condition may be indicated requiring the cap dispenser to beserviced.

The disclosed arrangement uses a simple mechanical system to pivot thewelding gun to move the electrodes out of the work area of the weldingcell. Stand-alone electrode maintenance tools and simple translationstages achieve a total solution that is easy to expand, more economical,and easier to maintain. Because the maintenance tools do not have afootprint within the robot envelope, they do not affect or require anyof the reach of the robot. The maintenance tools are not exposed to thehazards and contamination found within the welding cell. The robot cellis not exposed to the hazards and contamination that may occur at themaintenance tools. The maintenance tools may be made accessible forservice while the robot is cycling.

The maintenance tools are moved to defined positions so there is norequirement for position variation compensation schemes, such as springcentered slides, which can contribute to erratic machining results inthe prior art due to chattering.

Movement in the plane perpendicular to the taper axis minimizes thepossibility a side force could be applied to the taper surfaces, whichcould inhibit the taper separation. Movement in the direction of thetaper axis ensures the tapers can separate without the need for externalforce or movement.

The design includes a simple round orifice that is less sensitive toelectrode geometry variation such as the diameter or surface conditionof the electrode cap. It also does not rely on the accessible surface ofthe taper or of electrode. The design is much simpler than others whichemploy shafts, gears, cams, and motors. This reduces the cost andimproves the operational reliability.

The linear dispensers can be made to accommodate a variety of electrodecap sizes. Spring loaded pins are employed to latch the linear dispenserinto its holder and to retain the drawer in the closed position.Therefore, the functions of filling and replacing the dispenser may beeasy accomplished independently.

Filling may be performed off line if desired. During filling, thedispenser can be held at an orientation that best exploits gravity toaid the process. The length of the exposed opening during loading canalso be coordinated to minimize the opportunity for electrodes to tipover, if their geometry predisposes them to do so. The action of closingof the dispenser, applies spring pressure that will be used to urge thecap electrodes towards the opening.

Replacement of the dispenser can be performed to minimize interactiontime or for convenience. It can also be done to change the electrodegeometry if a changeover is performed to enable the robot cell toproduce different weldments.

It should also be understood that although a particular componentarrangement is disclosed in the illustrated embodiment, otherarrangements will benefit herefrom. Although particular step sequencesare shown, described, and claimed, it should be understood that stepsmay be performed in any order, separated or combined unless otherwiseindicated and will still benefit from the present invention.

Although the different examples have specific components shown in theillustrations, embodiments of this invention are not limited to thoseparticular combinations. It is possible to use some of the components orfeatures from one of the examples in combination with features orcomponents from another one of the examples.

Although an example embodiment has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of the claims. For that reason, the following claimsshould be studied to determine their true scope and content.

What is claimed is:
 1. A cap extractor for a welding gun comprising: a housing; a pair of springs; and first and second arms arranged between the springs, each of the first and second arms having teeth configured to engage a welding cap, the first and second arms configured to move relative to the housing in first and second directions transverse to one another by deflecting the springs.
 2. The cap extractor of claim 1, wherein the first and second arms are mounted to spaced apart disks, the first and second arms pivotally connected to one another by a spacer pin that rotationally affixes the disks to one another.
 3. The cap extractor of claim 2, wherein the springs are wave springs, each wave spring received in a recess of one of the disks, and a collar is arranged between each disk and the housing to locate a respective wave spring relative to the housing.
 4. The cap extractor of claim 1, wherein an actuator is pivotally attached to the housing, the actuator operatively connected to the first arm to rotate the first and second arms along with the disks, the actuator configured to articulate relative to the housing during rotation of the first arm in the housing.
 5. The cap extractor of claim 1, wherein a biasing spring is interconnected to the first and second arms to urge the first and second arms toward one another.
 6. A method of removing a cap from a welding gun comprising the steps of: receiving a welding cap having a centerline between teeth of first and second arms; floating the arms along the centerline and laterally relative to the centerline during the receiving step to permit alignment between the teeth and the welding cap; and twisting the welding cap from a welding gun.
 7. The method of claim 6, comprising the step of normally biasing the first and second arms toward one another, and the receiving step separates the first and second arms.
 8. The method of claim 7, wherein one of the first and second arms abuts a stop preceding the receiving step, and the one of the first and second arms is spaced from the stop during the twisting step.
 9. The method of claim 6, wherein the first and second arms are supported between disks, and comprising the step of supporting the disks by springs, and the floating step includes deflecting at least one of the springs.
 10. The method of claim 6, wherein an actuator is pivotally mounted to a housing containing the first and second arms, and the twisting step includes articulating the actuator relative to the housing and rotating the first and second arms relative to the welding gun.
 11. The cap extractor of claim 3, wherein the wave springs are configured to permit the discs to float laterally with respect to the housing enabling the first and second arms to float laterally relative to the housing.
 12. The cap extractor of claim 3, wherein the wave springs are configured to permit the discs to float vertically with respect to the housing enabling the first and second arms to float vertically relative to the housing.
 13. The cap extractor of claim 1, wherein the housing includes a first aperture one side and a second aperture on an opposite side of the one side, the first and second apertures configured to receive first and second weld caps arranged opposite one another on a weld gun.
 14. The cap extractor of claim 2, wherein additional spacer pins separate and affix the disks to one another, one of the additional spacers received in a slot in the second arm.
 15. The cap extractor of claim 2, wherein the housing includes a stop configured to limit the travel of the second arm during rotation via a stop pin carried on the second arm. 